from bs4 import BeautifulSoup

html_doc = """
<html><head><title>The Dormouse's story</title></head>
<body>
<p class="title"><b>The Dormouse's story</b></p>

<p class="story">Once upon a time there were three little sisters; and their names were
<a href="http://example.com/elsie" class="sister" id="link1">Elsie</a>,
<a href="http://example.com/lacie" class="sister" id="link2">Lacie</a> and
<a href="http://example.com/tillie" class="sister" id="link3">Tillie</a>;
and they lived at the bottom of a well.</p>

<p class="story">...</p>
"""

#soup = BeautifulSoup(html_doc)
#print(soup.prettify())

with open('tmp') as f:
    html_doc = f.read()

soup = BeautifulSoup(html_doc)
once_value = ''
for input_label in soup.find_all('input'):
    if input_label.get('name') == 'once':
        once_value = input_label.get('value')
        break
print once_value
